Automated traffic signals are operated by electronic field signal controllers according to a signal timing plan for each controlled location, such as an intersection of two streets. The timing plans are developed in part by traffic volume counting, for example, and often they are very outdated, and therefore cause undue delay of vehicle-users of the intersection among other problems. The need remains for better optimized traffic signal timing plans to reduce delay and the concomitant wastes of time and energy expended when vehicles are unduly delayed at an intersection.
Glossary: Some of the terms used herein may be defined as follows.
Traffic Signal or simply “Signal”. Refers to a set of traffic control devices (hardware and software) generally deployed at a single street intersection, highway ramp or other location. A traffic signal is controlled by an associated Field Signal Controller (“FSC”).
Field Signal Controller (“FSC”). Refers to a controller, generally comprising electronics and/or software, arranged to control a Traffic Signal. The Field Signal Controller may be located at or near the corresponding Traffic Signal location, such as a street intersection, or at a central traffic management center, or some combination of the two. An FSC may operate according to various rules, algorithms, and inputs, depending on the location and circumstances of the signal it controls. The traffic signal controller that acts as the “brains” of the traffic signal. The controller tells the signal what to run, how long to run, when to run, etc. The controller collects information from the intersection through the detection system, decides how to respond, and then tells the vehicle and pedestrian displays or “indicators” how to operate.
Field Signal Controller State. Refers to the state of an FSC, for example, the status of one or more internal timers, and the state or status of one more “indicators” (see below), controlled by the FSC such as vehicle displays. The FSC has a given state at a specific time.
Cycle Time or Cycle Length. An FSC may change state according to a Cycle Time, although the cycle time may not always be constant. For example, a weekday cycle time may differ from a weekend cycle time for a given FSC. The cycle time generally, for a fixed schedule timing plan, is the time to cycle through all of the states of the timing plan. More detail is provided later.
Detector. Refers to an electrical, magnetic, optical, video or any other sensor arranged to provide raw input signals to an FSC in response to detection of an entity such as a motor vehicle, transit vehicle, bicycle or pedestrian. The input signal may correspond to the arrival, presence, or departure of the vehicle. A detector also may be activated manually, for example, by a pedestrian or a driver pressing a button. Of course, a detector also may be initiated remotely or wirelessly, similar to a garage or gate opener. In general, Detectors provide raw inputs or stimuli to an FSC.
Indicator. Refers to one or more displays or other visible and/or audible indicators arranged to direct or inform a user such as a motor vehicle driver, bicyclist, pedestrian, or transit vehicle operator at or near a given traffic signal location. A common Indicator for motor vehicles is the ubiquitous Green-Yellow-Red arrangement of lights. Typically, an indicator is triggered or otherwise controlled by the FSC associated with the signal location.
Signal Timing Plan (or simply Timing Plan) refers to a plan or scheme that determines the sequence of operation, i.e. state changes, time periods (for example, red light and green light time periods) and various other parameters for controlling an intersection by operation of signals, while considering approaching and/or present vehicles, as well as time for pedestrians and other users. A timing plan generally is implemented in software code or a database, and the plan is utilized by an FSC to control its operations. So, as a very simple example, to increase the green time for a particular phase during rush hour, one would modify the signal timing plan for that intersection accordingly. Some traffic signals operate on a fixed schedule, while some others are “actuated” or may be adaptive to various conditions and/or detector inputs.